1. Field of the Invention
This invention relates to a process of producing a methylphenyltrisiloxane having the following general formula [I]: ##STR3## wherein R.sub.1 and R.sub.2 may be the same or different and are each a methyl or phenyl group.
2. Description of the Prior Art
Methylphenyltrisiloxanes having the above general formula [I], for example, 1,3,3,5-tetramethyl-1,1,5,5-tetraphenyltrisiloxane, are widely used as silicone oil for oil diffusion pumps and are of industrial use.
For the production of a methylphenyltrisiloxane having the general formula [I], there has been known, for example, a process in which methyldiphenylsilanol is condensed with dimethyldichlorosilane or methylphenyldichlorosilane with hydrochloric acid being eliminated in the presence of a dehydrochlorinating agent comprising an organic amine compound such as pyridine, trialkylamine, etc. to synthesize a methylphenyltrisiloxane compound having R.sub.1 and R.sub.2 corresponding to the diorganodichlorosilane used (Refer to U.S. Pat. No. 2,890,234 and Nakayama et al.: Shinkuh (Vacuum), 13(2), 59-63 (1970)).
Another process has also been known in which sodium methyldiphenylsilanolate is prepared from methyldiphenylsilane, and is reacted with dimethyldichlorosilane or diphenyldichlorosilane to produce a methylphenyltrisiloxane compound having R.sup.1 and R.sup.2 corresponding to the diorganodichlorosilane used (Sec U.S. Pat. No. 3,523,131).
However, the process according to U.S. Pat. No. 2,890,234 and the process by Nakayama et al. involve the use of an organic amine compound in excess of the amount stoichiometrically equivalent to the methyldiphenylsilanol to be reacted therewith, and requires a greater space in the reactor accordingly. In addition, these processes produce large amounts of solid amine hydrochlorides as by-products, with the resultant lowering in the stirrability of the reaction system. It has been necessary, therefore, to add a large amount of solvent to the reaction system in order to obviate the lowering in stirrability. With such requirements, the processes are very low in yield per unit volume of a reactor and extremely poor in productivity. Furthermore, the processes have the problem of complicated steps, because the large amounts of amine hydrochlorides must be treated and the synthesized methylphenyltrisiloxane, having an amine odor and a pale yellow or a yellow color, requires deodorizing and decoloring steps for conversion into an odorless and colorless product. Thus, these processes have difficulties as to economy and operability.
The method according to U.S. Pat. No. 3,523,131, on the other hand, has the problem that the synthesizing process is long and that gaseous hydrogen, which is flammable and very difficult to deal with, is generated in large amounts during the preparation of the sodium methyldiphenylsilanolate as an intermediate.